Electric resistance heating elements



NOV. 4, 1969 R AY, JR ET AL 3,476,862

ELECTRIC RESISTANCE HEATING ELEMENTS 2 Sheets-Sheet l Filed May 16, 1968 INVENTORS EDWARD N. CYRWA): JR. WILL/AM J. METALS/(Y A TTORNEY Nov. 4, 1969 E. N. CYRWAY, JR, ET AL 3,476,862 I ELECTRIC RESISTANCE HEATING ELEMENTS Filed May 16. 1968 2 She ets-Sheet z /05 awn r095 DWA/?0 N. crew/1 1 JR.

WILL/AM J- METAL sxrr ATTORNEY Arm BY I United States Patent O U.S. C]. 1325 Claims ABSTRACT OF THE DISCLOSURE Resistance heating elements particularly suited for use in high temperature vacuum and other furnaces which comprise, for each element, a plurality of thin strips of tungsten metal in laminar arrangement, secured together with tantalum wire and having reinforced electrical contact points.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to resistance heating elements for use in vacuum and other high temperature furnaces.

Description of the prior art In the treatment of metal parts for use in space vehicles and other extreme service applications the parts must be thoroughly and completely heated to a high temperature in a relatively neutral atmosphere or vacuum, and then cooled or quenched at a selected rate.

Heating elements of tungsten have heretofore been used for furnace heating. One example of elements used in vacuum furnaces is that shown in the U.S. Patent to Charles A. S. Hill, No. 3,155,758, where interlocking elements of tungsten strip in a cage like structure are shown. While such a structure is useful in the quantity of tungsten required in a large furnace of the present type with the Hill structure would make it prohibitively expensive.

Tungsten is a very difiicult metal to work and cannot be bent unless it is thin. Thick sheets will crack along the bend line rendering them useless for heating. With the elevated temperatures involved and the quantity of heat required a single thickness of element will not provide sufficient heat and may warp or sag under load. The heating element of the present invention provides ample heat, is readily fabricated and overcomes the disadvantage of prior elements.

SUMMARY OF THE INVENTION The present invention relates to resistance heating elements for use in vacuum and other furnaces where high heat is required which elements are composed of formed strips of tungsten metal secured together in laminar arrangement.

The principal object of the present invention is to provide resistance heating elements for vacuum furnaces that will have a long useful life, are easily fabricated, and will be free from other difliculties heretofore encountered in this field.

It is a further object of the present invention to provide resistance heating elements for vacuum furnaces which are sturdy in construction and free from difficulties in use.

It is a further object of the present invention to provide resistance heating elements for vacuum furnaces which accommodate to the elevated temperatures with minimum distortions, and which are fabricated and supported in a manner which decreases the likelihood of failure.

It is a further object of the present invention to provide resistance heating elements for vacuum furnaces which 3,476,862 Patented Nov. 4, 1969 "ice are free from expansive restraints and which have increased current carrying capacity.

It is a further object of the present invention to provide resistance heating elements for vacuum furnaces which are assembled without Welding, brazing, or other metal fusion operations.

Other objects and advantageous features of the invention will be apparent from the description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS The nature and characteristic features of the invention will be more readily understood from the following description taken in connection with the accompanying drawings forming part thereof, in which:

FIGURE 1 is a view in perspective of a plurality of heating elements of the present invention in place in a furnace;

FIG. 2 is a view in perspective of one form of a single heating element of the present invention;

FIG. 3 is an enlarged vertical sectional view taken approximately on the line 33 of FIG. 2;

FIG. 4 is an enlarged view in perspective of another form of a single heating element of the present invention;

FIG. 5 is a side elevational view of the element shown in FIG. 4; and

FIG. 6 is a vertical sectional view taken approximately on the line 6-6 of FIG. 4.

It should, of course, be understood that the description and drawings herein are illustrative merely, and that various modifications and changes can be made in the structure disclosed without departing from the spirit of the invention.

Like numerals refer to like parts throughout the several views.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularly to the drawings and FIGS. 1 to 3 thereof, a plurality of heating elements 10 are shown in place in FIG. 1 in a typical furnace installation with the interior space in the furnace (not shown) indicated in broken lines. The elements 10 are composed of a plurality of strips 11 of thin tungsten metal. in the embodiment illustrated each of the strips 11 is of a thickness of ten one-thousandths (0.010) of an inch and of a width of one and one-half inches. In this thickness the tungsten can be readily formed by bending and without breakage. The strips 11 each have fiat horizontal bottom members 12 with opposite vertical side wall members 13 connected thereto, horizontal inwardly extending top members 14 connected to side members 13 and vertical electrical connecting portions 15. In a particular embodiment there are five strips 11, as shown more clearly in FIGS. 2 and 3, which are retained or held together at intervals by coils 16 of wire which may be of tungsten or tantalum metal and free to expand when heated relative to the expansion of the strips 11. The wire may be of approximately thirty-thousandths (0.030) of an inch in diameter in the embodiment illustrated.

The connecting portions 15 are each provided with a pair of contact plates 18 located respectively on the inside and outside strips 11 of the element 10 to provide a reinforced connection for attachment to a source of electrical energy (not shown). As shown in FIG. 1 the bottom members 12 of the elements 10 are supported on horizontal bars 20 which extend lengthwise inside the furnace (not shown) and are engaged by vertical rods 21. The rods 21 are mounted to the furnace (not shown) in wellknown manner and so as to remain stationary and not transfer heat out of the furnace interior.

The elements 10 are additionally supported in suspension at their top members 14 by horizontal bars 22 carried by hangers 23 mounted in the wall of the furnace (not shown). The elements are free to slide along and across bars and 22 during heating and cooling and are not restrained from such movement by the bars.

The vertical connecting portions 15 with contact plates 18 are each engaged by horizontally extending buss bars 25 which are secured to plates 18 by screws 26 and plates 27. The buss bars 25 extend to a source of electrical energy (not shown) for energizing the elements 10.

Referring now more particularly to FIGS. 4 to 6 of the drawings another form of heating element 100 is there illustrated. The element 100 is comprised of a plurality of strips 111 like the strips 11 heretofore described and in addition has horizontal and vertical retainers 101 and 102 and spacers 103 to provide enhanced strip retention and performance.

The retainers 101 and 102 and spacers 103 are formed of tungsten metal and may be of twice the thickness of one of the strips 111. The retainers 101 are located between the innermost second and third strips 111 at their top members 114 and also at their bottom members 112 between the horizontal furnace bars 20. The retainers 101 are formed of two U-shaped plates 105 which have center section 106 and vertically extending flanges 107 on each side of section 106. The retainers 101 have the plates 10": oriented so that the pairs of flanges 107 on sections 106'- extend in opposite directions. Holes 108 are provided in center section 106 adjacent flanges 107 to permit coils 116 of tungsten or tantalum wire to pass therethrough and retain the strips 111 and retainers 101 together.

The retainers 102 are of the same configuration as retainers 101 but of greater length and with an additional pair of holes 108. The retainers 102 are located between the innermost second and third strips 111 at the side members 13.

The spacers 103 are located at the four corners of the element 100, are of L-shaped configuration and of the same thickness as retainers 101 and 102.

The spacers 103 contact the ends of the elements 101 and 102 serving to hold them in place and provide support for the strips 111 at the corners.

The elements 100 have connecting portion 115 with contact plates 118 thereon for connection to a source of electrical energy (not shown) as described for element 10.

It should be noted that the elements 10 or 100 and strips 111 or 11 may be used for temperatures from room temperature to about 4,000 F. and the elements 10 or 100 and strips 11 or 111 do not sag or droop from the heat. The elements 10 and 100 have been observed to sustain an electrical energy input of 70 kw. without distortion.

In fabricating the elements 10 and 100 the strips 11 or 111 are individually bent to the configuration shown and described in the specification and drawing and the strips 11 or 111 assembled together by securing with coils 1-6 of tungsten or tantalum wire. The plates 18 are also secured with a coil 16 of tungsten or tantalum wire, the resulting elements 10 and 100 since they did not require welding or fusion treatment, permits of long continued operation as no strain points are present and therefore there is no failure due to expansion and contraction of the strips 11 or 111.

It will thus be seen that structure has been provided with which the objects of the invention are attained.

We claim: 1. A resistance heating element for use in a high temperature furnace which comprises a plurality of continuous strips of metal in laminar arrangement, said strips each having a horizontal bottom portion, opposite vertical side portions extending upwardly from the bottom portion, horizontal portions extending inwardly from the side portions, and vertical electrical connecting portions extending upwardly from said horizontal portions, and retaining means at spaced locations on said strips holding the strips against relative displacement. 2. A resistance heating element as definedin claim 1 in which said metal strips are of tungsten. 3. A resistance heating element as defined in claim 2 in which said strips are of a thickness of the order of ten onethousandths of an inch. 4. A resistance heating element as defined in claim 3 in which said strips are of a width of the order of one and one half inches. 5. A resistance heating element as defined in claim 1 in which said retaining means is coils of tungsten wire. 6. A resistance heating element as defined in in which said retaining means is coils of tantalum wire. 7. A resistance heating element as defined in claim 1 in which said electrical connecting portions at their upper ends have at least one plate of tungsten secured thereto. 8. A resistance heating element as defined in claim 1 in which said electrical connecting portions have supporting members connected thereto. 9. A resistance heating element as defined in claim 8 in which said horizontal portions have additional supporting members in engagement therewith. 10. A resistance heating element as defined in claim 1 in which said retaining means is a plurality of spaced retainers of U shape with coils of wire extending through holes therein and around said strips; and spacers are provided to bridge the space between said retainers.

claim 1 References Cited UNITED STATES PATENTS 3,263,015 7/1966 Hill 13-25 BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner US. Cl. X.R. 2 19-55 2 

